The present invention relates to an actuator assembly for an information storage media. In particular, it relates to a rotary electromagnetic actuator assembly for use in positioning read/write heads on a data storage device.
In information storage systems, for example, in a magnetic disk recording system, or a hard disk drive (HDD), magnetic read/write heads are used to read/write data information from/to the data storage disks. The disk surfaces are divided into a plurality of tracks or annular bands for storing data information. The read/write heads are supported close to the corresponding disk surfaces by a head positioning/turning assembly, e.g., an actuator assembly. The read/write heads are carried by the actuator assembly and are movable above the disk surface for reading/writing data information.
Recently, the hard disk drive industry has been placing considerable emphasis upon high magnetic recording density hard disk systems exhibiting (1) higher data storage capacity at lower cost per bit of stored data, and (2) high data storage throughput at lower power. As is well known, the bit recording density of disks is the product of the number of flux reversals per unit length of a track (i.e. linear bit density) multiplied by the number of tracks per inch (TPI). Presently, the commercial hard disk products in the market, which commonly employ a conventional planar moving-coil actuator assembly as shown in FIG. 1, generally have a track density of 6000xcx9c8000 TPI. The head positioning system of a commonly used HDD supported by the conventional actuator assembly has a cross-over frequency of only 500xcx9c700 Hz, which can only support the track density up to 12000xcx9c14000 TPI. Achieving high track density (25000 TPI or higher) is a major challenge for the designers of head positioning systems and corresponding servo systems.
A prior art moving-coil actuator assembly shown in FIG. 1 comprises a voice coil 1, a carriage arm 2, a suspension and head gimbal assembly (HGA) member 3 and a pivot member 4. Electromagnetic actuating force FA is generated at an end of the carriage arm 2 to actuate the head positioning assembly. Due to the non-coupled electromagnetic actuating force FA generated, there is an inherent reaction force FR exerted on the pivot member 4. This reaction force FR will excite a considerable and undesirable resonance vibration in the actuator assembly about the pivot member in a data track seeking direction. This vibration is called a Quasi-Rigid (QR) body vibration mode and is usually located at mid band frequency band, e.g., 4xcx9c6 KHz. The servo bandwidth of the head positioning assembly is therefore limited by this in-plane resonance vibration mode.
The prior art techniques and the corresponding problem inherently existed in conventional actuator systems as described in a variety of patents and publications. For example, although U.S. Pat. No. 4,476,404 to P. A. Bygdnes, et al., U.S. Pat. No. 4,635,151 to H. B. Hazebrouck, et al., U.S. Pat. No. 5,027,242 to H. Nishida, et al., and U.S. Pat. No. 5,566,375, disclose different techniques and methods to improve operating characteristics of rotary actuator systems, respectively, the constructions adopted and embodied in the corresponding patents will inherently excite the reaction force exerted on the pivot member. Thus, there is unexpected variation and deterioration of positioning characteristics of actuator system.
A similar approach to this problem was first disclosed in U.S. Pat. No. 4,620,252 issued Oct. 28, 1986 to R. C. Bauck, et al. There, a twin planar coil was first adopted. The twin coils are rigidly fixed and displaced symmetrically at the other end of the carriage of a head positioning mechanism. A similar approach to adopting a twin planar coil attached to the other end of a carriage arm was also disclosed in U.S. Pat. No. 5,486,965 to Yoshida, et al. However, it is noticed that the reaction force is still exerted on the pivot member due to the fact that the actuating force generated by the other two effective portions of the twin coil is not perpendicular to the seeking direction of the actuator system such as to excite resonance vibration in the actuator system within mid-band of frequency. Also, it is a complex structure in a rotary actuator system and is likely to have many difficulties in manufacturing and assembly.
Another similar approach to this problem was disclosed in one of the embodiments of U.S. Pat. No. 5,295,031 to K. G. Wasson, et al. There, a moving-magnet type construction is used to couple a torque into a pivotally mounted arm member and the unexpected reaction force imposed at the pivot shaft and bearing associated therewith are substantially minimized to improve the accuracy of positioning. However, it is noticed that there is an inherently considerable bias force and hysteresis in the moving-magnet type actuator systems. Further, exposure of magnets in the moving-magnet actuators lead to many difficulties in manufacturing and assembly processes.
The foregoing and other objects, features and advantages of the invention will be better understood from the following more detailed description and appended claims.
It is a first aspect of the present invention that the actuator assembly disclosed can generate pairs of forces substantially orthogonal to the moving direction of the read/write heads and therefore generate substantially no reaction force to the pivot member of the carriage arm assembly, so that the QR body vibration mode can be substantially suppressed and an improved servo bandwidth can be obtained.
It is a second aspect of the present invention that the actuator assembly disclosed has a voice coil and corresponding magnets which are structurally as simple as conventional voice coil and magnets, and therefore only limited additional cost is added in manufacturing by an actuator assembly of the present invention.
According to the first and second aspects recited above, the present invention discloses an actuator assembly for positioning a plurality of read/write heads above an information storage media, such as a data storage disk. The actuator assembly comprises a carriage arm assembly movably mounted on a pivot and having a voice coil mounted thereon, and a magnetic device having a plurality of poles for generating a magnetic field. The voice coil further comprises at least one effective portion for interacting with the magnetic field to generate at least one pair of driving forces in a direction substantially orthogonal to a moving direction of the read/write heads. The magnetic field further comprises a first magnetic region and a second magnetic region, the second magnetic region being in a direction opposite to the first magnetic region and the voice coil being placed with the at least one effective portion crossing through the first and the second magnetic regions.
The actuator assembly of the present invention is structurally simple for low cost manufacturing and effectively improves the read/write heads positioning accuracy in a data storage system.